Solar energy charge controllers are in charge. A solar panel pumps electricity into a battery that stores it. But the solar panel has no control over how much it does or how the battery receives it. A solar panel just performs under the parameters upon which it was built. It’s the charge controller, sometimes called a charge regulator that is positioned between the solar panel and the battery that regulates the voltage and the current and essentially halts charging activity temporally when necessary.

Solar panels are connected through an Array Combiner (if you have one) to the charge controller. The charge controller is connected to the battery.

Array Combiners

Array Combiners, also called an Array Combiner Box or Combiner Box: First, an array of solar panels could mean one panel or multiple panels. If you have multiple panels, even in a small system, it means a lot of wires to deal with, positive and negative from each panel. One way or another, those wires need to be combined into one positive and one negative string or wire to connect to the charge controller. Array combiners are used to combine that input from those multiple strings (wires) into one output circuit of positive and negative. These boxes can be quite sophisticated with breakers, monitoring characteristics, etc. so they can also be expensive. Most are intended to run big systems.

These sophisticated boxes might be considered overkill for very small systems. Some alternatives are to build your own or use ring terminals connecting them together with a nut and bolt. Ex: All the positive wires connected to one larger positive wire with an appropriately sized nut and bolt. The second option will work, just looks rather like a rodents nest. (There certainly could be another option I don’t know about.)

I put together an Array Combiner based on the following instructions. It works great. Solar panel wires connect to the Array Combiner Box. Wires from the Array Combiner Box attach to the Charge Controller.

Back to charge controllers . . .

The solar electrical charge controller controls the incoming charge to the battery. More complex/sophisticated charge controllers do even more. Your system cannot function without one. Any battery being charged, even with a small solar panel, can be over charged and destroyed given enough time without a charge controller.

As mentioned, the only time you may not need a charge controller is when using a 1-5 watt panel as a trickle charger. The intention of a trickle charger is to replace normal energy loss in a battery that occurs from just sitting. The general rule is that if a trickle charge panel puts out 2 watts or less per 50 battery amp hours you don’t need a charge controller. But, when in doubt, use one. Small ones are inexpensive.

The generally accepted industry standard on charge controllers today is the three stage unit meaning a three stage charge cycle. This type is put out by a variety of good companies. One and two stage units are old and rely on shunt transistors or relays. Basically “shunt” controllers just disconnect the panel. You don’t see many of these old ones around except perhaps in inexpensive solar “kits” (The “wow great value” with the included (crappy) charge controller!) or on old systems. Just know you can do a lot better if you run into one. (And if you get one you’ll probably want to replace it.)

Three stage units, the current standard, have three stages of charge - bulk, absorption and float. They don’t just simply turn things on and off. Many other features, many standard, others optional by model, may be included as well. Some of these features have great benefit to the battery.

Some of these features are:

Reverse current protection – eliminates the current running in reverse, out of the battery, at night when the panels aren’t working.

PWM series charging - means Pulse Width Modulation. Acts as a very rapid on off switch to check the state of charge and what needs to be done. It adjusts, modifies and does it.

Equalization – a feature where the unit attempts to make all cells in the battery of equal value bringing them all up to full capacity. This activity also can stir up battery liquid keeping the acid and water mixed.

Sense terminals – a feature where a pair of sense terminals will “look” and compare battery voltage to what the charge controller is putting out and have the charge controller compensate if necessary.

LVD or Low Voltage Disconnect – some units have “Load” or “LVD” output which can be used for small load devices, like a small light. With LVD this output will automatically disconnect to keep from running the battery down too far. The automatic disconnect is most useful for sites where the small load is unattended. It isn’t recommended to connect inverters to this output directly on the charge controller unless it’s very small.

Choosing a Solar 12v Charge Controller

Charge controllers come in all sorts of sizes as determined by number of amps with a variety of features as mentioned above and more. Since they’re sold by the number of amps and solar panels are sold by watts and the charge controller needs to be able to handle the watts put out by the solar panel, it’s helpful to repeat the equation, amps x volts = watts, but not always the most accurate method here.

A 4.5 amp charge controller is considered “small”. 4.5 amps x 12 volts (battery) = 54 watts according to the math. Putting math aside however, the most accurate thing to do is just read the amp rating off the solar panel specs. It will be listed there. It’s an alternate measurement to watts. Other influences affect the amps put out by a solar panel that may change the real amp outcome. Comparing amps to amps is better.

A small charge controller, like a 4.5 amp, three stage with many features, costs in the $25 or so area. Charge controllers can also cost over $500 so there’s a multitude of choices in-between depending on the size of your system. If you anticipate starting small but think getting more solar panels may be in your future, get a charge controller big enough to accommodate the potential increase. Too small a controller won’t work, a bigger than needed unit works fine.